1. Field of the Invention
The present invention relates to vibration isolator equipment that can isolate a load such as a vibration sensitive instrument from a surface such as a floor of a building.
2. Background of the Invention
For vibration sensitive instruments, the relative motion between two surface induced by vibration can cause errors and reduce accuracy. For example, in the case of a fine resolution microscope, the highly magnified images of a part under inspection are captured and analyzed. If the floor onto which the system is situated undergoes vibrating movement that can be transferred to the instrument, the induced vibration may cause a relative displacement between the two surfaces where the microscope and parts are mounted. Such relative displacement causes the captured images to be too flurry for accurate analysis. To minimize this problem, the equipment incorporates vibration isolators to reduce or prevent the floor vibration from being transferred to the instrument. The most commonly used isolators are active air isolators that are effective and low in cost. With low throughput equipments, where the length of time taken for the system to resettle after a gross disturbance induced to the instrument is not a critical concern, the air isolation table including a highly damped table platform and several active air isolators are sufficient.
However, in a manufacturing process involving automated equipments with fast moving components, the system is subjected to constant acceleration and deceleration of a large mass and shifting center of gravity, those induce gross disturbance to the system. The reduction of resettling time required to eliminate these gross disturbance becomes a key factor since the productivity improves with shortened process cycle time. Furthermore, in this application, the process includes many steps of exchanging parts between devices mounted on different platforms, such as a fully automated apparatus wherein a robotic system mounted on a non-isolated platform fetches and retrieves parts between the instrument and an input/output station. Therefore, it is desirable to bring and lock the instrument to an equilibrium position, referred as the home position, so that the robotic assembly can quickly locate the parts. In summary, the vibration isolator for these applications needs to address the three following critical requirements:
Reduce or prevent the floor vibration, in vertical and horizontal directions, from being transferred to the instrument,
Minimize the resettling time after each gross disturbance,
Bring and secure the instrument to an equilibrium home position.
With the addition of the last two requirements, an air isolation table becomes inadequate since it takes a long period of time, in order of several seconds to damp out all gross disturbances and resume its leveled position, especially with an instrument having a high center of gravity. To counter this problem, a much larger table is used to increase the mass of the table platform and spicing between the air isolators. This will lead to big increases in cost, weight and footprint of the equipment.
U.S. Pat. No. 5,000,415 issued to Sandercock disclosed an active vibration isolator assembly that includes a plurality of piezoelectric actuators that can vary the distance between the load and the floor surface to compensate for the movement of the floor. U.S. Pat. No. 5,660,255 issued to Schubert et al. disclosed a vibration isolator that has a number of piezoelectric actuators to isolate a load in a vertical direction and additional piezoelectric actuators to isolate the load in a horizontal plane. Such active isolation system may meet all three requirements. However, it has a prohibited cost and complexity due to expensive actuator assemblies and complex feedback servo control systems.
U.S. Pat. No. 6,209,841 issued to Houghton, Jr., et al. disclosed a vibration isolator that has an active isolator assembly as disclosed by Sandercock to isolate the load in a vertical direction and a passive isolator assembly including a pendulum to provide isolation in a horizontal plane. Such system may significantly reduce the cost of the vibration isolator with respect to the isolators of Schubert et al., but still is very complex and expensive in comparison with an active air system.
The present invention provides a novel approach meeting all above three critical requirements that may be satisfied by an active piezoelectric isolator system, but with the cost and simplicity of an active air isolator assembly.
The object of this invention is to provide a vibration isolator that prevents the floor movement from being transferred to a load and minimizes gross disturbances induced by rapid motions of the load, but without the drawbacks that are found in the prior arts.
The apparatus of the present invention comprises an isolator assembly including a parallelogram mechanism that isolates the load in a first direction while maintaining said load leveled and a passive isolator that isolates the load in a second direction or directions.
This and other objects and advantages of this invention will become apparent through examining the following description of the arrangement and construction of the constituent components and appended claims in conjunction with the attached drawings.